1. Field of the Invention
This invention relates to a layout of auxiliary mechanisms for an engine which are driven by the crankshaft of the engine by way of a driving belt.
2. Description of the Prior Art
As is well known, the auxiliary mechanisms for the engine, e.g., a compressor for an air conditioner, an alternator, an oil pump for a power-steering system, a cooling water pump and the like are driven by an auxiliary mechanism driving belt which is a V-belt such as a V-ribbed belt passed around the crank pulley and pulleys for the auxiliary mechanisms. See Japanese Unexamined Utility Model Publication No. 62(1987)-143045, for instance.
When the tension on the auxiliary mechanism driving belt is too high, durability of the auxiliary mechanism driving belt and the auxiliary mechanisms is deteriorated. On the other hand, when the tension on the auxiliary mechanism driving belt is too low, excessive slip occurs, which leads to production of noise.
Recently, production of belt noise due to fluctuation in revolution of the crank pulley caused by torque fluctuation which is due to increase in load of the auxiliary mechanisms and/or the condition of combustion in the engine has become a serious problem.
Generally, the noise of the auxiliary mechanism driving belt is apt to be produced when the load of the auxiliary mechanisms is increased while the tension on the auxiliary mechanism driving belt is low, and this tendency is especially strong in the automatic transmission vehicle in which the inertia moment of the crankshaft is small and factors which can promote fluctuation in the engine revolution such as fluid resistance exist. As the noise of the auxiliary mechanism driving belt, there have been known noise which is produced due to slip of the belt in the radial direction of the pulley and noise which is produced due to slip of the belt in the tangential direction of the pulley. In the case of the V-ribbed belt, it is considered that the noise is produced mainly due to the slip of the belt in the tangential direction of the pulley in view of the fact that the slip of the belt in the radial direction of the pulley is less and the noise is produced only when the tension on the belt is low.
FIG. 11 shows the relation between the peripheral speeds of the crankshaft pulley, the air conditioner compressor pulley and the auxiliary mechanism driving belt and the crank angle (the engine revolution). As can be understood from FIG. 11, the noise is produced in synchronization with the fluctuation in the engine revolution and at about 45 degrees ATDC, that is, immediately after combustion. Simultaneously with the production of the noise, the belt speed becomes lower than the peripheral speed of the crank pulley.